Axial flow compressor



Oct. 9, 1962 J. B. MARSDEN 3,057,543

AXIAL FLOW COMPRESSOR Filed Feb. 5, 1960 2 Sheets-Sheet l INVENTOR 3JOHN B. MARSDEN F 6. 2 B

Oct. 9, 1962 J. B. MARSDEN AXIAL FLOW COMPRESSOR 2 Sheets-Sheet 2 FiledFeb. 5, 1960 INVENTOR JOHN B. MARSDEN BY HIS AT ORNEY Patented Oct. 9, 1962 United States Patent Oflice 3,057,543 AXIAL FLOW COMPRESSOR John B.Marsden, Painted Post, N.Y., assignor to Ingersoll-Rand Company, NewYork, N.Y., a corporation of New Jersey Filed Feb. 5, 1960, Ser. No.6,987 3 Claims. (Cl. 230-143) The present invention relates generally toaxial compressors, pumps, blowers and the like, and more particularly tothat type wherein rotary members engage in screw and thread relationshipand the pumped or compressed fluid follows an axial spiral paththerebetween.

Such members, which are the core of such machines generally operate on apair of parallel longitudinal shafts, vertically co-planar, within afully enclosed casing except for the usual inlet and outlet ports, suchas shown in Patent #2,287,716 issued to Whitfield on June 23, 1942.

This invention is directed more particularly to improvements in theassociated components thereof such as the provision of an end clearancechamber for purposes of unloading therein the compressed fluid trappedin the end clearance pocket, which would otherwise seep through thenormal clearance between the rotors and between the rotor ends and thechamber end wall, and means for directing this fluid back towards thelow pressure side of the compressor which also provides for conductingany water or other liquid entrapped therein out towards the low pressureside of the compressor. In this manner the compressor is now able tohandle a certain amount of liquid flow therethrough, otherwise suchentrapped liquid would normally prevent escape of the trapped gasesthrough the normal clearance between the rotors, and in extreme casestend to distort the precise relationship between the rotors and causephysical damage to the compressor.

Devices of the herein described nature generally have two helicallythreaded rotors supported on and revolving about parallel axes, with thethreads of the rotors continuously intermeshing to thereby define acontinuous seal line for the full extent of their engagement. The casingencloses both of the members and the crests or perimetral edges of thethreads of the rotary members also form seals with the inner surface ofthe casing. The end wall of the casing forms a seal with the end facesof the rotary members. Therefore any flow of fluid from one end of themembers to the other must pass through the grooves between the threadsof the rotary members. Due to the sealing thus described the threads ofthe members when they are rotated cooperate with each other and with thewalls of the casing to form fluid pockets that advance and move from oneend of the casing whereat the low pressure or intake port is lo cated,to the other end of the casing whereat the high pressure, or dischargeport is located.

In order to permit rotation of the members the threads must becomplementary. Thus the threads of one mem ber have a right hand helicaltwist, while the threads of the other member have a left hand helicaltwist.

One of the rotary members is commonly referred to as the main rotor. Thecomplementary rotary member is usually referred to as the gate rotor.

. In operation of the device, the threads in. the main rotor act as acontinuous series of pistons which slide axially in the same directionthrough the grooves of the gate rotor and produce a successive series ofpockets which convey the fluid from one end of the members to the other.

i When the trailing edge of the crest of the main rotor on the end ofthe rotor at the discharge port, crosses the intersection of the boresof the casing, a pocket is formed bounded by the leading flank of themain rotor lobe and the trough of the gate and the end plate of thecasing. As the main rotor revolves the fluid entrapped in this pocket iscompressed. There being no escape for this fluid other than the normalclearance between the rotors, an undesirable condition is set up. Acertain amount of extra horsepower is required to compress the entrappedfluid to a pressure necessary to force it through the normal clearancebetween the rotors thereby reducing the efliciency of the compressor.While the trapped pocket is formed on both ends of the compressor, thepocket on the discharge end is the only one of major importance, sincethe pocket on the inlet end is a low pressure pocket.

In the case of a non-compressible fluid being so entrapped, such as aliquid, or a fluid with a high liquid content, the threads of the weakerrotor, usually the gate rotor, may be deformed or actually broken.

The present invention contemplates overcoming the foregoing problem byproviding a pressure relief chamber in the end wall of the casing at thehigh pressure side and communicating with the enclosed pocket before thepocket is completely sealed off from the discharge port. The pressurerelief chamber extends across the lobes of the rotors and communicateswith the low pressure side of the compressor and/or the pockets of therotors which in turn are in communication with the intake port.

Thus at all times an escape path of sufiicient size is provided to allowevacuation of the entrapped fluid to the low pressure pockets of therotors without any undue pressure buildup.

The fluid thus evacuated is negligible in volume and does not noticeablyaffect the overall efiiciency of the compressor. The slight loss sosustained is less than that caused by normal manufacturing tolerances.

It is therefore one of the objects of this invention to prevent thepressure buildup due to the entrapped fluid in the aforementioned endpocket of the compressor, and to do so in a novel and etfective manner.

Another object of the invention is to provide means for evacuating theentrapped fluid in said end pocket over to a low pressure area of thecompressor.

Still another object of the invention is to increase the ability of thecompressor to pass a certain amount of liquid therethrough withoutdamage to the rotors.

The foregoing and other objects and advantages will become more apparentby a consideration of the drawings and the detailed description thatfollows, but it is to be understood that the drawings are for thepurposes of illustration only and do not in any way define the limits ofthe invention.

In the drawings:

FIGURE 1 is a side elevation of the compressor with the near face of thehousing removed,

FIGURE 2 is a section view taken along the line 2--2. of FIG. 1 in thedirection of the arrows,

FIGURES 3 to 6 are sections taken along the line 3--3 of FIG. 1, showingthe positions of the rotors during the interval of rotation when theentrapping pressure pocket is in communication with the pressure reliefchamber.

Referring now to the drawings and more particularly to FIGS. 1 and 2, ahousing 10 comprises an end plate 12. and an oppositely disposed endplate 14. The end plate 12 forms part of an inlet port 16 and the endplate 14 forms part of an outlet port 18. The housing 10 issubstantially in the form of a figure 8 in end view as shown in FIGS. 3to 6 inclusive, and is more specifically defined by two parallel bores21 and 23 having common intersections at 20 and 22 to form a commonchamber 25.

A helical main rotor 24 (FIG. 1) is rotatably mounted 3 on alongitudinal shaft 26 and is supported in bearings 28 and 30respectively encased in the end plates 12 and 14. A mating helical rotor32 usually called the gate rotor is mounted on a second longitudinalshaft 34, and supported in bearings 36 and 38 respectively encased inthe end plates 12 and 14.

The main rotor 24 in section is asymmetrical in form and comprises apair of lobes 40 and 42 the flanks of which are generated by the crestedges 44 of the gate rotor 32.

The grooves 46 of the mating gate rotor 32 are generated by the crestedges 48 of the main rotor lobes 40 and 42.

Thus the helical main rotor 24 and the helical gate rotor 32 mesh, andwhen rotated, form a continuous seal line, which moves diagonally acrossthe housing 10 from one end of the rotors to the other along thecomplete length thereof.

A pinion 33 mounted on the shaft 26 operatively engages a gear 35mounted on the shaft 34 to maintain a normal running clearance betweenthe mating elements of the main rotor 24 and the gate rotor 32.

In the normal operation of the device fluid is drawn into the inlet port16 by the action of the rotors, rotating in opposing directions to openthe pockets 49 and 51 of the mating main rotor 24 and gate rotor 32. Thepockets 49 and 51 continue to draw in fluid until they reach theirmaximum displacement, at which point they are cut off from the suctionport 16 and compression of the fluid begins as the rotors continue torotate. After a predetermined amount of internal compression hasoccurred, the pockets of the rotors now communicate with outlet port 18.

However, when the trailing crest edge 48 of the main rotor lobe 40passes beyond the intersection 22 of the bores 21 and 23 a pressurepocket 50 is formed between a leading flank of one of the main rotorlobes 40, a groove 46 of the gate rotor, and the inner surface of theend plate 14 as illustrated in FIG. 3, and as shown in longitudinaldepth by the area bounded between the lines X and Y in FIG. 1.

During certain applications the fluid compressed has a relatively highliquid content and as the fluid is transported through the device aportion of liquid is entrapped in the pocket 50. With no means forescape other than the normal running clearances between the partsdefining the pocket 50, major damage to the device would result from thecontinued rotation of the rotors, since the liquid is incompressible.

To avoid the foregoing consequences, a pressure relief chamber 52 isprovided in the end wall of the plate 14 on the opposite side from theoutlet port 18 (FIG. 2) that is in constant communication with the lowpressure side of chamber 25. The inboard boundary 54 of the chamber 52registers with the groove 46 of the gate rotor 32 when the rotors are inthe relative position shown in FIG. 3. At this point communication stillexists between the pocket 50 and the outlet port 18 through a passage 56in the end wall of the end plate 14. As the rotors continue to rotatethe flank of the groove 46 leaves the boundary edge 54 of the chamber 52providing communication between the pressure pocket 50 and the chamber52. As the passage to the discharge port grows smaller (FIGS. 4 and thecommunication with the chamber 52 increases providing a constant area ofthe passageway means for the escape of entrapped fluid and liquid. Inthis manner any substantial increase in the pressure of the entrappedfluid is prevented.

FIGS. 3 to 6 inclusive illustrate the progressive reduction of thepressure pocket 50, beginning from when the pocket initially is formed,and the rotors 24 and 32 continue to rotate, up until its completeevacuation of fluid into the pressure relief chamber 52.

It will be noted from these illustrations (FIGS. 3 to 6) that at eachand every one of the progressive stages of the pocket 50 the pressurizedfluid confined therein is provided with an escape path either to thedischarge port of the compressor as shown in FIG. 3, or over to the lowpressure areas of the compressor as shown in FIGS. 4, 5 and 6.

Thus, means are provided whereby the several objects of this inventionare achieved in a positive and effective manner. Although only oneembodiment of the invention has been illustrated and described, it willreadily be apparent to those skilled in the art, that changes andmodifications in the parts, and relative arrangement, may be madeWithout departing from the spirit and scope of the invention.

I claim:

1. A compressor comprising a casing having a chamber, a pair ofoppositely disposed end plates connected to said casing to close theends of the chamber, a pair of rotors disposed in the chamber betweensaid end plates, said chamber having an inlet at one axial end thereofon one side of a plane through the axes of rotation of both rotors andan outlet at its other axial end on the other side of said plane, saidrotors having complementary helical threads meshing with each other andoperating to cyclically define pressure pockets each being formed incommunication with the inlet and sequentially being blocked from theinlet then communicating with the outlet, each pressure pocket enlargingin volume during communication with the inlet to draw fluid therein andreducing in volume thereafter to compress the fluid then discharge thecompressed fluid through the outlet, one of said threads defininghelical lobes, the other of said threads defining helical grooves forreceiving the meshing lobes progressively from the inlet to the outletend of said compressor to provide seals between succeeding pressurepockets that move axially in the compressor tending to form fluid trapswhen such pockets are closed to said compressor outlet after discharge,and said end plate at the outlet end of said compressor having a recesson the inlet side of said plane being in constant communication withsaid compressor inlet and communicating with the ends of the fluid trapswhen formed to relieve trapped fluid therein to said compressor inlet.

2. A compressor in accordance with claim 1 in which, each of said lobeshas a leading and a trailing flank surface intersecting to provide acrest edge, each of said grooves has an arcuate surface generated by thecrest edges of said lobes and terminating at a crest edge that generatesthe leading flank surfaces of said lobes, said crest edges of meshinglobes and grooves forming seal lines with the surfaces they generatethat are spaced by a pocket of varying volume defined by the lobe andgroove disposed between the seal lines, and said pockets between thecrest edges forming the fluid traps when the crest edges form seal linesthat extend to the outlet ends of said rotors and close the formed trapsto the compressor outlet.

3. A compressor comprising a casing having a pair of intersectingparallel bores forming a chamber therein, a pair of oppositely disposedend plates connected to said casing to close the ends of said bores, apair of rotors disposed in said bores between the end plates, saidchamber having an inlet at one axial end thereof on one side of a planethrough the axes of rotation of both rotors and an outlet at its otheraxial end on the other side of said plane, said rotors havingcomplementary helical threads meshing with each other and operating tocyclically define pressure pockets each being formed in communicationwith the inlet and sequentially being blocked from the inlet thencommunictting with the outlet, each pressure pocket enlarging in volumeduring communication with the inlet to draw fluid therein and reducingin volume thereafter to compress the fluid then discharge the compressedfluid through the outlet, one of said threads defining helical lobes,the other of said threads defining helical grooves for receiving themeshing lobes progressively from the inlet to the outlet end of saidcompressor to provide seals between succeeding pressure pockets thatmove axially in the compressor tending to form fluid traps after suchpockets are closed to said compressor outlet, said end plate at theoutlet end of said compressor having a pair of recesses therein eachdisposed on one side of said plane, said recess disposed on the outletside of I said plane being in constant communication with the compressoroutlet and providing the last connection thereto from said pockets whensuch traps are being formed, and said recess on the inlet side of saidplane being in constant communication with said compressor inlet andcommunicating with the ends of the fluid traps when formed to relievetrapped fluid therein to said compressor inlet.

References Cited in the flle of this patent UNITED STATES PATENTSKauffrnan Dec. 20, 1932 Lysholm et al Mar. :22, 1938 Whitfield June 23,1942 Berck Nov. 28 1950 Montelius Dec. 11, 1951 Nilsson Dec. 9, 1952Whitfield June 16, 1953 Rathman Apr. 12, 1955 Dolza et al. May 22, 1956Erick et al Feb. 4, 1958 Meyer et a1 May 6, 1958 Kreamer Jan. 20, 1959Haberland May 12, 1959 Derntchenko Dec. 8, 1959 Whitfield May 2, 1961Oliver July 4, 1961 UNITED STATES PATENT OFFICE REGTION CERTIFICATE OFCOR Patent No, 3 057 ,543 October 9, 1962 John B. Marsden It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow. Column 4., iine 73 ,v for "eommunictting" read communicatingcolumn 6, line 16, under the heading "UNITED STATES PATENTS" for "2315876" read 2,915,976 "a y of August 1963,

d and sealed this 20th da Signe (SEAL) Attestr ERNEST w. SWIDER DAVID L.L D

Commissioner of Patents Attesting Officer

